Microelectromechanical systems (MEMS) devices are small devices used for example in accelerometers, gyroscopes, implemented in portable devices such as mobile phones, remote controllers, movement sensors or the like, where acceleration and/or velocity of the portable device can be measured. A MEMS device may include a mass suspended from a substrate and movable relative to the substrate, and an electromechanical transducer which converts external mechanical forces acting on the mass into measurable electrical signals. By measuring the electrical signals, the external mechanical forces acting on the mass, can be derived.
Mechanics of a MEMS accelerometer device can be modelled by a simple second order mass-spring system:maext=m{umlaut over (x)}+b{dot over (x)}+kx  (1)
where,
m is the mass,
aext is the external acceleration applied to the mass,
x is the mass displacement,
{dot over (x)} is the mass velocity,
{umlaut over (x)} is the mass acceleration,
k is the spring constant, and
b=2D√{square root over (k*m)} is the damping ratio.
In an un-damped MEMS accelerometer device, the mass may oscillate at a resonant frequency. In order to avoid undesired oscillations and thus prevent possible catastrophic effects on the mass and MEMS accelerometer device, the mass needs to be damped before measurement. By submerging the mass in viscous fluids, for example, friction of the mass can be controlled such that the mass is damped with damping ratio b in equation (1).
However, the amount of damping force applied is critical for the functionality of the MEMS accelerometer device. A MEMS accelerometer device described by equation (1) can have three different behaviours: if D>1 the device is overdamped, if 0<D<1, the device is underdamped, If D=1, the device is critically damped.
Overdamped MEMS accelerometer devices have a smaller settling time than underdamped MEMS accelerometer devices. Further, underdamped MEMS accelerometer devices can oscillate and eventually break.
As a consequence, overdamped MEMS accelerometer devices are preferred to underdamped MEMS accelerometer devices.
Critically damped MEMS accelerometer devices are ideally the best in class accelerometers because they can be damped very rapidly without oscillations.
Thus, there is a need for MEMS device which is more efficiently damped.